GUANTÁNAMO BAY NAVY BASE, Cuba — Soon after Osama bin Laden’s driver arrived at the Guantánamo prison in 2002, he told interrogators the identity of the al-Qaida chief’s most senior bodyguard, then a fellow prison-camp detainee.

But, inexplicably, the United States let the bodyguard go.

This startling information was revealed in the fourth day of the war-crimes trial of Salim Hamdan, 37, facing conspiracy and material-support-for-terrorism charges as an alleged member of bin Laden’s inner circle.

Michael St. Ours, an agent with the Naval Criminal Intelligence Service (NCIS), provided the first tidbit. He testified for the prosecution that his job as a prison-camps interrogator in May 2002 was to find and focus on the bodyguards among the detainees.

Hamdan helped identify 30 of them, 10 percent of the roughly 300 detainees then held here. They had just been transferred to Camp Delta from the crude compound called Camp X-Ray, and U.S. intelligence was trying to unmask all of them.

Chief among them was Casablanca-born Abdallah Tabarak, then 47, described by St. Ours as “a hard individual,” and, thanks to Hamdan, “the head bodyguard of all the bodyguards.”

St. Ours said he was eager to speak with Tabarak. But the Moroccan was “uncooperative,” and St. Ours moved on to other intelligence jobs — and never learned what became of him.

On cross-examination, Hamdan defense attorney Harry Schneider, of Seattle, dropped a bombshell: “Would it surprise you to learn he was released without ever being charged?”

St. Ours looked stunned.

“Yeah,” he said.

Prison-camp and Pentagon spokesmen did not reply Thursday to a request for an explanation. Tabarak’s name was gone from an official prison-camp roster drawn up by the Defense Department in September 2004, after some 200 captives had been sent away. A month before, Morocco’s state news agency said all five of its nationals had been repatriated from the camps.

For two days, FBI and other federal agents have testified about the extent — and limits — of Hamdan’s cooperation in a string of interrogations since his November 2001 capture by U.S.-allied Afghan forces at a checkpoint in southern Afghanistan.

Defense lawyers have sought to portray the father of two with a fourth-grade education as ultimately helpful to the Americans, after he initially covered up his relationship with bin Laden.

Prosecutors have called him truculent, a loyal and trusted member of bin Laden’s inner circle who grudgingly spoke with interrogators — and never came clean on why there were two surface-to-air missiles in his car when he was captured.

CIA advised on legal waterboarding

WASHINGTON — Lawyers for the Bush administration told the CIA in 2002 that its officers could legally use waterboarding and other harsh measures while interrogating al-Qaida suspects, as long as they acted “in good faith” and did not deliberately seek to inflict severe pain, according to a Justice Department memo made public Thursday.

The memo, apparently intended to assuage CIA concerns that its officers could someday face torture charges, said interrogators needed only to possess an “honest belief” that their actions did not cause severe suffering. The honest belief did not have to be based on reality.

“Although an honest belief need not be reasonable, such a belief is easier to establish where there is a reasonable basis for it,” stated the Aug. 1, 2002, memo signed by Jay Bybee, then an assistant attorney general with the Justice Department’s Office of Legal Counsel.

The memo was one of three released by the Justice Department under a Freedom of Information Act request filed by the American Civil Liberties Union (ACL). The heavily redacted memos offer insight into the administration’s legal maneuvering as it sought to justify the CIA’s program of aggressively interrogating high-level al-Qaida operatives held in secret prisons overseas. The program included measures intended to weaken resistance and coerce confessions.

While human-rights groups and legal experts have condemned tactics as tantamount to torture, the Justice memo argued no action could be considered torture unless it was deliberately intended to be.

ACLU officials attacked the documents’ logic. “The memos provide further evidence that the Office of Legal Counsel completely distorted the law in order to permit interrogators to use methods that the U.S. has historically viewed as war crimes,” said Jameel Jaffer, director of the ACLU National Security Project.